Methods of making metal matrix composite and alloy articles

ABSTRACT

In one aspect, methods of making freestanding metal matrix composite articles and alloy articles are described. A method of making a freestanding composite article described herein comprises disposing over a surface of the temporary substrate a layered assembly comprising a layer of infiltration metal or alloy and a hard particle layer formed of a flexible sheet comprising organic binder and the hard particles. The layered assembly is heated to infiltrate the hard particle layer with metal or alloy providing a metal matrix composite, and the metal matrix composite is separated from the temporary substrate. Further, a method of making a freestanding alloy article described herein comprises disposing over the surface of a temporary substrate a flexible sheet comprising organic binder and powder alloy and heating the sheet to provide a sintered alloy article. The sintered alloy article is then separated from the temporary substrate.

RELATED APPLICATION DATA

The present application is a divisional application pursuant to 35U.S.C. § 120 of U.S. patent application Ser. No. 13/832,635 filed Mar.15, 2013.

FIELD

The present invention relates to methods of making metal matrixcomposite and alloy articles and, in particular, to freestanding metalmatrix composite and alloy articles having complex geometry, thin wallstructure and/or thin cross-section.

BACKGROUND

Fabrication of hard alloy or metal matrix composite articles is alwayschallenging since brittleness typically increases with increasinghardness. Fabrication of hard alloy or metal matrix composite articleshaving complex geometry, thin wall thickness or thin cross-section isparticularly challenging. Fabrication techniques such as pre-forming bypowder pressing, extrusion or injection molding followed by sinteringare often employed for making such articles. However, given thelimitations of tooling and dies, articles produced according to thesemethods are usually not near-net shape, necessitating additionalsignificant green shaping, machining and processing.

Moreover, casting can be used for making articles of complex geometryand thick wall structure. Nevertheless, casting is mainly limited to asubset of metal and alloy systems suitable for such operations. For hardalloys and metal matrix composites, casting can be difficult. Further,mechanical working, such as hot rolling, is sometimes employed formaking thin metal or alloy sheets. Hard alloys and metal matrixcomposites are generally unsuitable for hot rolling due to the highhardness exhibited by these materials rendering them brittle and proneto crack formation during the working process. In view of thesedeficiencies, new methods of producing hard alloy and metal matrixcomposite articles, including articles of complex geometry, thin wallstructure or thin cross-section, are required.

SUMMARY

In one aspect, methods of making freestanding metal matrix compositearticles are described herein which, in some embodiments, can offeradvantages over prior methods. Advantages of methods described hereincan be fully exploited when fabricating metal matrix composite articlesand alloy articles of complex geometry, thin wall thickness and/or thincross-section. A method of making a freestanding composite articledescribed herein comprises providing a temporary substrate and disposingover a surface of the temporary substrate a layered assembly comprisinga layer of infiltration metal or alloy and a hard particle layer formedof a sheet comprising organic binder and the hard particles. The layeredassembly is heated to infiltrate the hard particle layer with the metalor alloy providing a metal matrix composite, and the metal matrixcomposite is separated from the temporary substrate. Infiltration alloy,in some embodiments, comprises nickel-based alloy, cobalt-based alloy,copper-based alloy, iron-based alloy, aluminum-based alloy ortitanium-based alloy. Further, in some embodiments, infiltration metalor alloy is added to the sheet comprising organic binder and the hardparticles and, therefore, is not provided as a separate layer in theassembly.

In another aspect, methods of making freestanding metallic articles aredescribed herein. The freestanding metallic articles can be of complexgeometry, thin wall structure and/or thin cross-section. A method ofmaking a freestanding metallic article comprises providing a temporarysubstrate and disposing over a surface of the temporary substrate asheet comprising organic binder and powder metal or powder alloy. Thesheet of organic binder and powder metal or powder alloy is heated toprovide a sintered metal or sintered alloy article, and the sinteredmetal or sintered alloy article is separated from the temporarysubstrate.

These and other embodiments are described in greater detail in thedetailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a freestanding metal matrix composite articleproduced according to one embodiment of a method described herein.

FIG. 2 illustrates a freestanding metallic article produced according toone embodiment of a method described herein.

DETAILED DESCRIPTION

Embodiments described herein can be understood more readily by referenceto the following detailed description and examples and their previousand following descriptions. Elements, apparatus and methods describedherein, however, are not limited to the specific embodiments presentedin the detailed description and examples. It should be recognized thatthese embodiments are merely illustrative of the principles of thepresent invention. Numerous modifications and adaptations will bereadily apparent to those of skill in the art without departing from thespirit and scope of the invention.

I. Methods of Making Freestanding Composite Articles

A method of making a freestanding composite article described hereincomprises providing a temporary substrate and disposing over a surfaceof the temporary substrate a layered assembly comprising a layer ofinfiltration metal or alloy and a hard particle layer formed of a sheetcomprising organic binder and the hard particles. The layered assemblyis heated to infiltrate the hard particle layer with the metal or alloyproviding a metal matrix composite, and the metal matrix composite isseparated from the temporary substrate.

Turning now to specific steps, methods described herein compriseproviding a temporary substrate and disposing over a surface of thetemporary substrate a layered assembly comprising a layer ofinfiltration metal or alloy and a hard particle layer formed of a sheetcomprising organic binder and the hard particles. A temporary substratecan comprise any material not inconsistent with the objectives of thepresent invention. In some embodiments, a temporary substrate is formedof a material substantially inert to the metal or alloy infiltrating thehard particle layer. A temporary substrate can also be coated with amaterial substantially inert to the metal or alloy infiltrating the hardparticle layer. Materials substantially inert to molten infiltrationmetal or alloy, in some embodiments, comprise one or more ceramic orrefractory materials including hexagonal boron nitride, alumina, silica,silicon carbide, zirconia, magnesium oxide, graphite coated withhexagonal boron nitride, other ceramics or combinations thereof.Additional materials substantially inert to molten infiltration metal oralloy can comprise graphite or alloys of various compositions havinglimited reactivity with the infiltration metal or alloy.

In being substantially inert to infiltration metal or alloy, a temporarysubstrate can be reusable. Alternatively, a temporary substrate can beconsumed in the fabrication of the composite article. In someembodiments, for example, the temporary substrate is not inert to theinfiltration metal or alloy and bonds with the composite article. Insuch embodiments, the temporary substrate can be machined away orotherwise sacrificed to provide the freestanding composite article.

The temporary substrate can have any shape and/or dimension forproviding freestanding composite articles of desired shape anddimension. In some embodiments, the temporary substrate is a die or moldproviding freestanding composite articles of complex geometries, shapesand/or contours. For example, the temporary substrate can provide afreestanding composite article curved surface(s), planar surface(s)and/or polygonal geometries. In some embodiments, the temporarysubstrate is a die or mold reflecting the final shape or near-finalshape of the freestanding composite article and facilitates providingthe freestanding composite article in near-net shape form uponseparation of the article from the temporary substrate. For example, insome embodiments, a freestanding composite article is a wear pad, andthe temporary substrate is of shape and dimension to provide the wearpad in near-net shape form upon separation from the substrate, therebyobviating or reducing further processing steps.

Further, in some embodiments, a substrate is provided in an array formatcomprising a one or two-dimensional array of dies or molds forfabricating freestanding composite articles. Arrayed substrates canfurther enhance production efficiencies realized herein by permittingthe fabrication of a plurality of freestanding composite articles in asingle fabrication cycle. In one embodiment, for example, a substrate isprovided in a tray format having a two-dimensional array of dies ormolds suitable for wear pad fabrication.

As described herein, a layered assembly is disposed over a surface ofthe temporary substrate, the layered assembly comprising a layer ofinfiltration metal or alloy and a hard particle layer formed of a sheetcomprising organic binder and the hard particles. The sheet can beflexible and cloth-like in nature. Organic binder of the sheet, forexample, can comprise one or more polymeric materials. Suitablepolymeric materials for use in the flexible sheet can comprise one ormore fluoropolymers including, but not limited to,polytetrafluoroethylene (PTFE).

Suitable hard particles carried by the sheet can comprise particles ofmetal carbides, metal nitrides, metal carbonitrides, metal borides,metal silicides, cemented carbides, cast carbides, other ceramics,intermetallics or mixtures thereof. In some embodiments, metallicelements of hard particles comprise aluminum, boron, silicon and/or oneor more metallic elements selected from Groups IIB, IIIB, IVB, VB, andVIB of the Periodic Table. Groups of the Periodic Table described hereinare identified according to the CAS designation.

In some embodiments, for example, hard particles comprise carbides oftungsten, titanium, chromium, molybdenum, zirconium, hafnium, tanatalum,niobium, rhenium, vanadium, boron or silicon or mixtures thereof. Hardparticles, in some embodiments, comprise nitrides of aluminum, boron,silicon, titanium, zirconium, hafnium, tantalum or niobium or mixturesthereof. Additionally, in some embodiments, hard particles compriseborides such as titanium di-boride, B₄C or tantalum borides or silicidessuch as MoSi₂ or Al₂O₃—SiN. Hard particles can comprise crushed cementedcarbide, crushed carbide, crushed nitride, crushed boride, crushedsilicide, ceramic particle reinforced metal matrix composite, siliconcarbide metal matrix composites or combinations thereof. Crushedcemented carbide particles, for example, can have 0.1 to 25 weightpercent metallic binder. Additionally, hard particles can compriseintermetallic compounds such as nickel aluminide.

Hard particles can have any size not inconsistent with the objectives ofthe present invention. In some embodiments, hard particles have a sizedistribution ranging from about 0.1 μm to about 2 mm. Hard particles canalso demonstrate bimodal or multi-modal size distributions. Hardparticles can also have any desired shape or geometry. In someembodiments, hard particles have spherical, elliptical or polygonalgeometry. Hard particles, in some embodiments, have irregular shapes,including shapes with sharp edges.

Hard particles can be present in the sheet in an amount sufficient toprovide the resulting freestanding metal matrix composite a hardparticle content of about 20 vol. % to 90 vol. %. In some embodiments,hard particles are present in the sheet in an amount sufficient toprovide the resulting freestanding metal matrix composite a hardparticle content of about 30 vol. % to 85 vol. %. Moreover, hardparticles can be present in the sheet in an amount sufficient to providethe resulting freestanding metal matrix composite a hard particlecontent of about 40 vol. % to 70 vol. %.

Hard particles are combined with the organic binder to fabricate thesheet carrying the hard particles. The organic binder and hard particlesare mechanically worked or processed to trap the hard particles in theorganic binder. In one embodiment, for example, hard particles are mixedwith 3-15 vol. % PTFE and mechanically worked to fibrillate the PTFE andtrap the hard particles. Mechanical working can include spinning,rolling, ball milling, stretching, elongating, spreading or combinationsthereof. In some embodiments, the flexible sheet comprising the hardparticles is subjected to cold isostatic pressing. In some embodiments,the sheet comprising organic binder and the hard particles is producedin accordance with the disclosure of one or more of U.S. Pat. Nos.3,743,556, 3,864,124, 3,916,506, 4,194,040 and 5,352,526, each of whichis incorporated herein by reference in its entirety.

The layer of infiltration metal or alloy can comprise any metal or alloynot inconsistent with the objectives of the present invention. Suitableinfiltration alloy, for example, can be braze alloy having a meltingpoint lower than that of the hard particles and having compositionalparameters for wetting and bonding to the hard particles while notwetting and/or not substantially interacting with the temporarysubstrate. Infiltration alloy, for example, can comprise nickel-basedalloys, cobalt-based alloys, copper-based alloys, iron-based alloys,aluminum-based alloys or titanium-based alloys. Suitable nickel-basedinfiltration alloy can have compositional parameters derived from TableI.

TABLE I Nickel-based infiltration alloys Element Amount (wt. %) Chromium0-30 Molybdenum 0-5  Niobium 0-5  Tantalum 0-5  Tungsten 0-20 Iron 0-6 Carbon 0-5  Silicon 0-15 Phosphorus 0-12 Aluminum 0-1  Copper 0-50 Boron0-6  Nickel BalanceIn some embodiments, nickel-based infiltration alloy can have acomposition selected from Table II.

TABLE II Nickel-based infiltration alloys Ni-Based Alloy CompositionalParameters (wt. %)  1 Ni-(13.5-16)% Cr-(2-5)% B-(0-0.1)% C  2Ni-(13-15)% Cr-(3-6)% Si-(3-6)% Fe-(2-4)% B—C  3 Ni-(3-6)% Si-(2-5)% B—C 4 Ni-(13-15)% Cr-(9-11)% P—C  5 Ni-(23-27)% Cr-(9-11)% P  6 Ni-(17-21)%Cr-(9-11)% Si—C  7 Ni-(20-24)% Cr-(5-7.5)% Si-(3-6)% P  8 Ni-(13-17)%Cr-(6-10)% Si  9 Ni-(15-19)% Cr-(7-11)% Si-)-(0.05-0.2)% B 10 Ni-(5-9)%Cr-(4-6)% P-(46-54)% Cu 11 Ni-(4-6)% Cr-(62-68)% Cu-(2.5-4.5)% P 12Ni-(13-15)% Cr-(2.75-3.5)% B-(4.5-5.0)% Si-(4.5-5.0)% Fe-(0.6-0.9)% C 13Ni-(18.6-19.5)% Cr-(9.7-10.5)% Si 14 Ni-(8-10)% Cr-(1.5-2.5)% B-(3-4)%Si-(2-3)% Fe 15 Ni-(5.5-8.5)% Cr-(2.5-3.5)% B-(4-5)% Si-(2.5-4)% Fe

Moreover, cobalt-based infiltration alloy can comprise additive elementsof chromium, nickel, boron, silicon, tungsten, carbon, phosphorus aswell as other elements. In some embodiments, cobalt-based infiltrationalloy has compositional parameters of Co-(15-19)% Ni-(17-21)% Cr-(2-6)%W-(6-10)% Si-(0.5-1.2)% B-(0.2-0.6)% C. In another embodiment,cobalt-based infiltration alloy has compositional parameters ofCo-(8-15)% Si or Co-(3.5-4.5)% B. Cobalt-based infiltration alloy canhave a composition of Co-(9-13)% P. Further, cobalt-based infiltrationalloys can have compositions falling within commercially availablecobalt-based alloy under STELLITE® and/or HAYNES® trade designations.

Copper-based infiltration alloy can comprise additive elements of nickel(0-50%), manganese (0-30%), zinc (0-45%), aluminum (0-10%), silicon(0-5%), iron (0-5%) as well as other elements including phosphorous,chromium, beryllium, titanium, boron, tin and/or lead. In someembodiments, Cu-based infiltration alloy can have a composition selectedfrom Table III.

TABLE III Cu-based infiltration alloy Cu-Based Alloy CompositionalParameters (wt. %) 1 Cu-(18-27)% Ni-(18-27)% Mn 2 Cu-(8-12)% Ni 3Cu-(29-32)% Ni-(1.7-2.3)% Fe-(1.5-2.5)% Mn 4 Cu-(2.8-4.0)% Si-1.5%Mn-1.0% Zn-1.0% Sn-Fe-Pb 5 Cu-(7.0-8.5)Al-(11-14)% Mn-2-4)%Fe-(1.5-3.0)% Ni

Iron-based infiltration alloy can comprise 0.2-6 wt. % carbon, 0-5 wt. %chromium, 0-37 wt. % manganese, 0-16 wt. % molybdenum and the balanceiron. In some embodiments, sintered iron-based alloy cladding has acomposition according to Table IV.

TABLE IV Iron-based infiltration alloy Fe-Based Alloy CompositionalParameters (wt. %) 1 Fe-(2-6)% C 2 Fe-(2-6)% C-(0-5)% Cr-(28-37)% Mn 3Fe-(2-6)% C-(0.1-5)% Cr 4 Fe-(2-6)% C-(0-37)% Mn-(8-16)% Mo

Additionally, aluminum-based infiltration alloys can be employed.Aluminum-based infiltration alloys can comprise alloying elements ofcopper, magnesium, manganese, silicon, tin, chromium, zirconium, lithiumand/or other elements. Aluminum-based alloy can have compositionalparameters falling within casting aluminum alloys designated from 1xx.xto 9xx.x, for example, 2xx.x alloys in which copper is the principalalloying element. Aluminum-based alloy can also have a compositionfalling within wrought aluminum alloys designated from 1xxx to 9xxx.

Further, suitable titanium-based infiltration alloys can havecompositional parameters derived from Table V.

TABLE V Titanium-based infiltration alloy Element Amount (wt. %)Zirconium 0-40 Copper 0-20 Nickel 0-25 Molybdenum 0-2  Titanium BalanceIn some embodiments, titanium-based infiltration alloy is selected fromTable VI.

TABLE VI Titanium-based Infiltration Alloy Ti-Based Alloy CompositionalParameters (wt. %) 1 Ti-37.5% Zr-15% Cu-10% Ni 2 Ti-37.5% Zr-15% Cu-10%Ni-1% Mo 3 Ti-24% Zr-16% Cu-16% Ni-0.5% Mo 4 Ti-26% Zr-14% Cu-14%Ni-0.5% Mo 5 Ti-(18-22)% Zr-(18-22)% Cu-(18-22)% Ni 6 Ti-(18-22)%Zr-(18-22)% Cu-(18-22)% Ni-1% Mo 7 Ti-15% Cu-25% Ni

Infiltration metal or alloy can be provided to the layered assembly as ametal or alloy sheet or foil. Alternatively, infiltration metal or alloycan be provided as metal or alloy chunk(s) or block(s). Further,infiltration metal or alloy can be provided in powder form and carriedby an additional sheet comprising organic binder of the layeredassembly. Powder infiltration metal or alloy carried by an additionalsheet can have any particle size not inconsistent with the objectives ofthe present invention. In some embodiments, powder infiltration metal oralloy has an average particle size less than 200 μm. For example, in oneembodiment, powder infiltration metal or alloy has an average particlesize less than 55 μm. Further, powder infiltration metal or alloycarried by the sheet can demonstrate bi-modal or multi-modal sizedistributions. Powder infiltration metal or alloy can be combined withorganic binder in the fabrication of a cloth-like sheet as describedabove.

After positioning over a surface of the temporary substrate, the layeredassembly is heated to infiltrate the hard particle layer with theinfiltration metal or alloy providing a metal matrix composite. In someembodiments, for example, the temporary substrate, hard particles andinfiltration metal or alloy of the layered assembly are heated to atemperature above the melting point of the infiltration metal or alloypermitting the metal or alloy to penetrate and/or infiltrate the hardparticle layer forming the metal matrix composite. Organic binder ofsheet(s) in the layered assembly is burned off or otherwise decomposedduring the heating process. The temporary substrate and layered assemblycan be heated in vacuum or under inert or reducing atmosphere to atemperature and for a time period sufficient for the metal or alloy topenetrate and/or infiltrate the hard particle layer forming a fullydense or substantially fully dense metal matrix composite.

The metal matrix composite is cooled for solidification of theinfiltration metal or alloy and subsequently removed from the substrate.As described herein, metal or alloy infiltrating the hard particlelayer, in some embodiments, does not substantially interact with thetemporary substrate facilitating separation of the metal matrixcomposite from the temporary substrate. The lack of interaction orreactivity between the infiltration metal or alloy and the substrate canalso render the substrate reusable. Further, the metal matrix compositecan be in near-net shape form when removed from the temporary substrate.

In some embodiments powder infiltration metal or alloy of the assemblyis carried by the sheet comprising the hard particles. In suchembodiments, powder infiltration metal or alloy and hard particles arecombined with the organic binder and worked into a cloth-like sheet asdescribed herein. The assembly including the sheet comprising organicbinder, powder infiltration metal or alloy and hard particles isdisposed over the substrate surface and heated to melt or partially meltthe infiltration powder metal or alloy providing the composite articleof hard particles disposed in matrix metal or matrix alloy. Uponcooling, the composite article is separated from the substrate.Freestanding composite articles produced according to methods describedherein can be fully dense or substantially fully dense. For example,infiltration of the hard particle layer with molten metal or alloyprovides a fully dense or substantially fully dense metal matrixcomposite. In contrast to prior techniques including pre-forming bypowder pressing, extrusion or injection molding followed by sintering,freestanding composite articles produced according to methods describedherein are not limited by constraints such as minimum thickness, maximumlateral dimension(s) and/or geometry. In some embodiments, for example,a freestanding composite article having a thickness or wall thicknessless than 0.5 mm can be produced without significant green shaping orpost-sintering machining as is required for such an article formed byprocesses employing pre-forming steps of powder pressing, extrusion ormolding.

Further, a near net-shape freestanding composite article having at leastone lateral dimension in excess of 500 mm or in excess of 1000 mm can beproduced easily according to methods described herein. Such large sizesoften present complications in pre-forming of pressing, extrusion orinjection molding thereby necessitating significant pre-forming shapingand/or post-sintering machining operations. Production of near-net shapefreestanding composite articles described herein, in some embodiments,is facilitated by shaping the flexible sheet comprising the organicbinder and the hard particles. The flexible sheet, for example, can besubjected to shape-forming operation(s) wherein the sheet is provided ashape or form reflecting the net shape and size of the free-standingcomposite article. Shape-forming operations can include, but are notlimited to, drawing, die cutting, stamping and punching.

Freestanding composite articles produced according to methods describedherein can demonstrate desirable wear, abrasion, erosion and/orcorrosion properties as well as desirable mechanical properties. In someembodiments, a freestanding composite article displays an average volumeloss (AVL) less than 20 mm³ according to ASTM G65 Standard Test Methodfor Measuring Abrasion using the Dry Sand/Rubber Wheel, Procedure A. Insome embodiments, a freestanding composite article displays an AVLaccording to Table VII.

TABLE VII AVL of freestanding composite article AVL of FreestandingComposite Article* (mm³) ≤20 ≤12 ≤10 ≤8 ≤6 2-20 3-12 *ASTM G65 StandardTest Method for Measuring Abrasion Using the Dry Sand/Rubber Wheel,Procedure A

Additionally, in some embodiments, a freestanding composite articleproduced according to methods described herein can demonstrate anerosion rate of less than 0.05 mm³/g at a particle impingement angle of90° according to ASTM G76-07—Standard Test Method for Conducting ErosionTests by Solid Particle Impingement Using Gas Jets. A freestandingcomposite article, in some embodiments, displays an erosion rate lessthan 0.04 mm³/g, less than 0.03 mm³/g or less than 0.02 mm³/g at aparticle impingement angle of 90° according to ASTM G76-07.

In some embodiments, wear, abrasion, erosion and/or corrosion propertiesof a freestanding composite article described herein can be enhanced byapplication of a refractory coating by chemical vapor deposition (CVD),physical vapor deposition (PVD), thermal spray or combinations thereof.For example, a freestanding composite article can be coated withdiamond, diamond-like carbon or ceramic material(s) by CVD.Additionally, a freestanding composite article can be coated with ametal or alloy of lower melting point than the composite article. Such ametal or alloy coating can be operable for brazing the freestandingcomposite article to one or more structural components. Alternatively, afreestanding composite article described herein can be coated with epoxyor other organic material for bonding with other structural components.

II. Methods of Making Freestanding Metallic Articles

In another aspect, methods of making freestanding metallic articles aredescribed herein. A method of making a freestanding metallic articlecomprises providing a temporary substrate and disposing over a surfaceof the temporary substrate a sheet comprising organic binder and powdermetal or powder alloy. The sheet of organic binder and powder metal orpowder alloy is heated to provide a sintered metal or sintered alloyarticle, and the sintered metal or sintered alloy article is separatedfrom the temporary substrate.

Turning now to specific steps, a method of making a metallic articlecomprises providing a temporary substrate and disposing over a surfaceof the temporary substrate a sheet comprising organic binder and powdermetal or powder alloy. Suitable temporary substrates can comprise anytemporary substrate described in Section I herein. In some embodiments,for example, the temporary substrate is a mold or die formed of orcoated with a material substantially inert to the powder metal or powderalloy during sintering operations described further herein. For example,materials substantially inert to the powder metal or powder alloy undersintering operations can comprise one or more refractory materialsincluding hexagonal boron nitride, alumina, silica, silicon carbide,zirconia, magnesium oxide, graphite coated with hexagonal boron nitride,other ceramics or combinations thereof. Additional materialssubstantially inert to the powder metal or alloy under sinteringconditions can comprise graphite or alloys of various composition havinglimited reactivity with the sintered metal or alloy, such as hightemperature tungsten-based alloys, molybdenum-based alloys andchromium-based alloys. In being substantially inert to the powder metalor powder alloy during sintering operations, the temporary substrate canbe reusable. Additionally, the temporary substrate can have any shapeand/or dimension for providing freestanding metallic articles of desiredshape and dimension.

A sheet comprising organic binder and powder metal or powder alloy isdisposed over the substrate. As described in Section I, the sheet can becloth-like and flexible in nature. In some embodiments, organic binderof the sheet comprises one or more polymeric materials. Suitablepolymeric materials for use in the sheet can include one or morefluoropolymers including, but not limited to, polytetrafluoroethylene(PTFE).

Powder alloy carried by the sheet can be selected to producefreestanding articles of sintered nickel-based alloy or sinteredcobalt-based alloy. Sintered nickel-based alloy articles can havecompositional parameters derived from Table VIII.

TABLE VIII Nickel-based sintered alloy Element Amount (wt. %) Chromium0-30 Molybdenum 0-28 Niobium 0-6  Tantalum 0-6  Cobalt 0-15 Tungsten0-15 Iron 0-50 Carbon 0-5  Manganese 0-2  Silicon 0-10 Titanium 0-6 Aluminum 0-1  Copper 0-50 Boron 0-5  Phosphorus 0-10 Nickel BalanceIn some embodiments, for example, a sintered nickel-based alloy articlecomprises 18-23 wt. % chromium, 5-11 wt. % molybdenum, 2-5 wt. % totalof niobium and tantalum, 0-5 wt. % iron, 0-5 wt. % boron and the balancenickel. Alternatively, a sintered nickel-based alloy article comprises12-20 wt. % chromium, 5-11 wt. % iron, 0.5-2 wt. % manganese, 0-2 wt. %silicon, 0-1 wt. % copper, 0-2 wt. % carbon, 0-5 wt. % boron and thebalance nickel. A sintered nickel-based alloy article can comprise 3-27wt. % chromium, 0-10 wt. % silicon, 0-10 wt. % phosphorus, 0-10 wt. %iron, 0-2 wt. % carbon, 0-5 wt. % boron and the balance nickel. Asintered nickel-based alloy article can also incorporate phosphorus,silver, zinc, vanadium and/or other elements as alloying elements.

Moreover sintered cobalt-based alloy articles derived from powder alloycarried in the sheet can have compositional parameters selected fromTable IX.

TABLE IX Cobalt-based sintered alloy Element Amount (wt. %) Chromium5-35 Tungsten 0-35 Molybdenum 0-35 Nickel 0-20 Iron 0-25 Manganese 0-2 Silicon 0-5  Vanadium 0-5  Carbon 0-4  Boron 0-5  Cobalt BalanceIn some embodiments, sintered cobalt-based alloy articles derived frompowder alloy of the sheet have compositional parameters selected fromTable X.

TABLE X Co-based sintered alloy Co-Based Alloy Cladding CompositionalParameters (wt. %) 1 Co-(15-35)% Cr-(0-35)% W-(0-20)% Mo-(0-20)%Ni-(0-25)% Fe-(0-2)% Mn-(0-5)% Si-(0-5)% V-(0-4)% C-(0-5)% B 2Co-(20-35)% Cr-(0-10)% W-(0-10)% Mo-(0-2)% Ni-(0-2)% Fe-(0-2)% Mn-(0-5)%Si-(0-2)% V-(0-0.4)% C-(0-5)% B 3 Co-(5-20)% Cr-(0-2)% W-(10-35)%Mo-(0-20)% Ni-(0-5)% Fe-(0-2)% Mn-(0-5)% Si-(0-5)% V-(0-0.3)% C-(0-5)% B4 Co-(15-35)% Cr-(0-35)% W-(0-20)% Mo-(0-20)% Ni-(0-25)% Fe-(0-1.5)%Mn-(0-2)% Si-(0-5)% V-(0-3.5)% C-(0-1)% B 5 Co-(20-35)% Cr-(0-10)%W-(0-10)% Mo-(0-1.5)% Ni-(0-1.5)% Fe-(0-1.5)% Mn-(0-1.5)% Si-(0-1)%V-(0-0.35)% C-(0-0.5)% B 6 Co-(5-20)% Cr-(0-1)% W-(10-35)% Mo-(0-20)%Ni-(0-5)% Fe-(0-1)% Mn-(0.5-5)% Si-(0-1)% V-(0-0.2)% C-(0-1)% B

Sintered cobalt-based alloy of an article described herein can havechromium-rich carbide particles, molybdenum carbides, tungsten carbides,other carbides or hard intermetallic phase (Laves phase) present in themicrostructure or can be a solution-type alloy in which alloyingelements diffuse into the cobalt matrix. Alternatively, sinteredcobalt-based alloy of an article can demonstrate a microstructure freeor substantially free of such carbide particles or intermetallic phase,wherein alloying elements remain in solid solution without phaseseparation or precipitation during solidification.

Powder alloy carried by the sheet can be provided in pre-alloyed formhaving parameters for producing freestanding sintered nickel-based alloyand sintered cobalt-based alloy articles of desired composition. In someembodiments, pre-alloyed powders can be used to produce any of thefreestanding sintered nickel-based or sintered cobalt-based alloyarticles described above. For example, in some embodiments, pre-alloyedpowder carried by the sheet can have compositional parameters selectedfrom Table VIII, IX or X herein. Further, pre-alloyed nickel-basedpowders for use in methods described herein are commercially availableunder the HASTELLOY®, INCONEL® and/or BALCO® trade designations.Pre-alloyed cobalt-based powders for use in methods described herein arecommercially available under the trade designations STELLITE®,TRIBALOY®, HAYNES®, MEGALLIUM® and/or other trade designations.

Powder metal or powder alloy of the sheet can have any particle size notinconsistent with the objectives of the present invention. In someembodiments, powder metal or powder alloy has an average particle sizeof less than 200 μm. For example, in one embodiment, powder metal oralloy has an average particle size less than 55 μm. Further, powdermetal or alloy can demonstrate bi-modal or multi-modal sizedistributions. Powder metal or powder alloy can be combined with organicbinder in the fabrication of a cloth-like sheet as described above.

After positioning over a surface of the temporary substrate, the sheetcomprising organic binder and powder metal or powder alloy is heated toprovide the sintered metal or sintered alloy article. Organic binder ofthe sheet is burned off or otherwise decomposed during the heatingprocess. The temporary substrate and sheet comprising organic binder andpowder metal or powder alloy can be heated in vacuum or under inert orreducing atmosphere. Further the substrate and powder metal or powderalloy can be heated to a temperature and for a time period sufficient tosinter the metal or alloy into an article of freestanding form. Theresulting sintered metal or sintered alloy article, in some embodiments,is fully dense or substantially fully dense.

The sintered metal or sintered alloy article is cooled and subsequentlyremoved from the substrate. As described herein, the metal or alloy, insome embodiments, does not substantially interact with the temporarysubstrate during sintering operations, thereby facilitating separationof the sintered metal or sintered alloy article from the temporarysubstrate. In some embodiments, the sintered metal or sintered alloyarticle is in near-net shape form when removed from the temporarysubstrate.

In contrast to articles fabricated by prior techniques such aspre-forming by powder pressing, extrusion or injection molding followedby sintering, articles produced according to methods described hereinare not subject to dimensional and/or geometrical limitations imposed bytooling or dies required in prior powder processes. For example, in someembodiments, a freestanding sintered metal or alloy article of complexshape and thickness or wall thickness of less than 0.5 mm can be formedby methods described herein. Further, a sintered metal or alloy sheetproduced according to methods described herein can have at least onelateral dimension in excess of 500 mm or in excess of 1000 mm whiledemonstrating a thickness less than 1 mm. The ability to produce alloyarticles of such dimensions according to methods described herein isparticularly useful since many alloys are not mechanically workable,even at high temperature. Cobalt-based alloys containing carbideparticles or intermetallic particles, for example, are not suited formechanical working into articles of thin cross-section and large lateraldimension.

In some embodiments, freestanding metallic articles fabricated accordingto methods described in this Section II are near-net shape. As describedherein, production of near-net shape freestanding metallic articles canbe facilitated by shaping the flexible sheet comprising the organicbinder and the hard particles. The flexible sheet, for example, can besubjected to shape-forming operation(s) wherein the sheet is provided ashape or form reflecting the net shape and size of the free-standingmetallic article. Shape-forming operations can include, but are notlimited to, die cutting, stamping and punching.

Further, a freestanding sintered metal or sintered alloy article can becoated with one or more refractory materials to enhance abrasion,erosion, corrosion or other properties. For example, a freestandingsintered metal or alloy article can be coated with diamond, diamond-likecarbon or ceramic material(s) by CVD, PVD, thermal spray or othercoating methods. In some embodiments, a freestanding sintered metal oralloy article is coated with a metal or alloy composition. Such a metalor alloy coating can be operable for brazing the freestanding sinteredmetal or alloy article to one or more structural components.Alternatively, a freestanding sintered metal or alloy article describedherein can be coated with epoxy or other organic material for bondingwith other structural components.

EXAMPLE 1

A free standing composite tubular article was produced according to amethod described herein as follows. Tungsten carbide powder (40% byvolume 2 to 5 microns size particles and 60% by volume-325 mesh sizeparticles) was mixed with 6% by volume of PTFE. The mixture wasmechanically worked to fibrillate PTFE and trap the tungsten carbideparticles, thus making a cloth-like flexible abrasive carbide sheet asfully described in U.S. Pat. No. 4,194,040. A braze metal filler powderwith composition of 79-84% nickel, 13-19% chromium and 2-5% boron byweight was mixed with 6% by volume of PTFE to form another cloth-likebraze sheet, similar to that of tungsten carbide sheet set forth above.

The cloth-like carbide flexible sheet was applied to a cylindricalgraphite bar on the outer diameter surface, which was pre-coated with alayer of ceramic powder like hexagonal boron nitride, followed by gluingthe braze filler sheet in place over the tungsten carbide sheet. Thesample was then debindered and heated in a vacuum furnace to 1100°C.-1160° C. for approximately 15 minutes to 4 hours during which thebraze preform melted and infiltrated in the tungsten carbide sheet.After cooling, the cylindrical graphite bar was released to provide asubstantially fully densified composite tube of about 1.5 mm in wallthickness. FIG. 1 is the picture of the composite tube component.

EXAMPLE 2

An alloy sheet of waving contour was produced according to a methoddescribed herein as follows. −270 mesh STELLITE® 12 alloy powder oralloy powder with a composition of 28-32 wt. % chromium, 6-10 wt. %tungsten, 1-2 wt. % carbon, 0.2-0.5 wt. % boron, up to 4 wt. % nickel,up to 4 wt. % iron, up to 3 wt. % silicon, and up to 2% molybdenum wasblended with 6 vol. % PTFE and was mechanically worked to fibrillatePTFE and trap the alloy particles, thus making a cloth-like flexiblesheet. The cloth-like flexible sheet was placed on a graphite substratewith waving surface contour, which was pre-coated with ceramic powderlike alumina, followed by debindering and heating in a vacuum furnace toa temperature of 1160-1200° C. and holding for 20 minutes to 2 hours toprovide a substantially fully dense sheet of waving contour. FIG. 2shows the alloy sheet of waving contour having composition within therange of STELLITE® 12 alloy. An advantage of this method describedherein is its simplicity to make the sheet component of complex contour,large size and thin cross-section.

Various embodiments of the invention have been described in fulfillmentof the various objects of the invention. It should be recognized thatthese embodiments are merely illustrative of the principles of thepresent invention. Numerous modifications and adaptations thereof willbe readily apparent to those skilled in the art without departing fromthe spirit and scope of the invention.

That which is claimed is:
 1. A method of making a freestanding compositearticle comprising: providing a temporary substrate; disposing over asurface of the temporary substrate a layered assembly comprising a layerof cobalt-based infiltration alloy and a hard particle layer formed of aflexible sheet comprising organic binder and the hard particles; heatingthe layered assembly to infiltrate the hard particle layer with thecobalt-based infiltration alloy providing a metal matrix composite; andseparating the metal matrix composite from the temporary substrate. 2.The method of claim 1, wherein the hard particles comprise one or moremetal carbides, metal nitrides, metal carbonitrides, metal borides,metal silicides, crushed cemented carbides, cast carbides or mixturesthereof.
 3. The method of claim 1, wherein the cobalt-based infiltrationalloy comprises 15-19 wt. % nickel, 17-21 wt. % chromium, 2-6 wt. %tungsten, 6-10 wt. % silicon, 0.5-1.2 wt. % boron, 0.2-1.0 wt. % carbonand the balance cobalt.
 4. The method of claim 1, wherein thecobalt-based infiltration alloy comprises 20-35 wt. % chromium, 0-10 wt.% tungsten, 0-10 wt. % molybdenum, 0-2 wt. % nickel, 0-2 wt. % iron, 0-2wt. % manganese, 0-5 wt. % silicon, 0-2 wt. % vanadium, 0-0.4 wt. %carbon, 0.5-5 wt. % boron and the balance cobalt.
 5. The method of claim1, wherein the hard particles are present in the metal matrix compositein an amount of 20 vol. % to 90 vol. %.
 6. The method of claim 1,wherein the metal matrix composite is fully dense.
 7. The method ofclaim 1, wherein the organic binder comprises one or more polymericmaterials.
 8. The method of claim 1, wherein the cobalt-basedinfiltration alloy is in powder form and disposed in an additional sheetcomprising organic binder.
 9. The method of claim 1, wherein thecobalt-based infiltration alloy is provided as a sheet.
 10. The methodof claim 1, wherein the cobalt-based infiltration alloy is provided as achunk.
 11. The method of claim 1, wherein the metal matrix composite hasa thickness or wall thickness of 100 μm to 20 mm.
 12. The method ofclaim 11, wherein one or more surfaces of the metal matrix composite areshaped by the substrate.
 13. The method of claim 1, wherein thetemporary substrate is reusable.
 14. The method of claim 13, wherein thetemporary substrate is formed of or coated with a material substantiallyinert to the cobalt-based alloy infiltrating the hard particle layer.15. A method of making a freestanding metallic article comprising:providing a temporary substrate; disposing over a surface of thetemporary substrate a flexible sheet comprising organic binder andcobalt-based powder alloy; heating the sheet comprising the organicbinder and the cobalt-based powder alloy to provide a sinteredcobalt-based alloy article; and separating the sintered cobalt-basedalloy article from the temporary substrate.
 16. The method of claim 15,wherein the sintered cobalt-based alloy comprises 5-35 wt. % chromium,0-35 wt. % tungsten, 0-35 wt. % molybdenum, 0-20 wt. % nickel, 0-25 wt.% iron, 0-2 wt. % manganese, 0-5 wt. % silicon, 0-5 wt. % vanadium, 0-4wt. % carbon, 0-5 wt. % boron and the balance cobalt.
 17. The method ofclaim 15, wherein the sintered cobalt-based alloy comprises 15-35 wt. %chromium, 0-35 wt. % tungsten, 0-20 wt. % molybdenum, 0-20 wt. % nickel,0-25 wt. % iron, 0-2 wt. % manganese, 0-5 wt. % silicon, 0-5 wt. %vanadium, 0-4 wt. % carbon, 0-5 wt. % boron and the balance cobalt. 18.The method of claim 15, wherein the sintered cobalt-based alloycomprises 20-35 wt. % chromium, 0-10 wt. % tungsten, 0-10 wt. %molybdenum, 0-2 wt. % nickel, 0-2 wt. % iron, 0-2 wt. % manganese, 0-5wt. % silicon, 0-2 wt. % vanadium, 0-0.4 wt. % carbon, 0-5 wt. % boronand the balance cobalt.
 19. The method of claim 15, wherein the sinteredcobalt-based alloy comprises 5-20 wt. % chromium, 0-2 wt. % tungsten,10-35 wt. % molybdenum, 0-20 wt. % nickel, 0-5 wt. % iron, 0-2 wt. %manganese, 0-5 wt. % silicon, 0-5 wt. % vanadium, 0-0.3 wt. % carbon,0-5 wt. % boron and the balance cobalt.
 20. The method of claim 15,wherein the organic binder comprises one or more polymeric materials.21. The method of claim 15, wherein the sintered cobalt-based alloyarticle has a thickness of 100 μm to 20 mm.
 22. The method of claim 15,wherein the sintered cobalt-based alloy article is near-net-shape. 23.The method of claim 15, wherein the temporary substrate is reusable.